Convertible band pass receiver



Aug. 16, 1932. A. MEISSNER CONVERTIBLE BAND PASS RECEIVER Filed Feb. 18,1951 di/TFU HUTFUT INVENTOR ALEXANDER MEiSSNER 'AT'T RNEY Patented Aug.16, 1932 UNITED STATES PATENT OFFICE ALEXANDER MEISSN'ER, OF BERLIN,GERMANY, ASSIGNOR 'IO TELEFUNKEN GESELL- N SCHAIFT FT jR DBAHTLOSETELEGRAPI-IIE M. B. H., 01 BERLIN, GERMANY, A COR- al PORATION OFGERMANY CONVERTIBLE BAND rAss nncnrvna App1icati0n filed, February 18,1931, Serial No. 516,586, and in. Germany February 6, 1 930.

The present inventionrelates to band pass receivers, and moreparticularly to a method of, and means for, operating a band pass rebandwidth must be constant throughout the whole frequency range. Sincedifierent broadcast transmitters are usually only about 10,000 cyclesapart it follows that the frequency band admissible for the receiveramounts to only 10,000 cycles. Hence, the point is that, upon changingthe wave of the receiver from 200 meters to, say, 600 or 800 meters, theaccepted frequency band should be 10,000-cycles throughout.

This requirement is not fulfilled with receivers of the kind heretoforeknown. The receivers have mostly been so built that alternately a tunedcircuit and a tube followed each other. But this insures merely greaterselectance, in other words, greater tuning sharpness the frequency bandwidth changed from wave length to wave length. Indeed, for a constantinductive coupling adjustment, it is so much larger the shorter the wavelength. Now, this inconvenience may be obviated in the following manner.

Two tuned circuits, on the one hand, are in constant inductive couplingrelationship, while, on the other hand, they are coupled capacitively bya condenser which is invariable throughout the entire frequency range.The condenser is chosen so large that, in the presence of the highfrequency for which the tuning condensers are very small, it playspractically no part as regards the coupling between the two circuits,though playing a decisive part so far as the coupling at the lowerfrequency is concerned. It is thus possible to create conditions so thatfor the whole frequency range the accepted frequency band width willremain substantially constant.

It has, heretofore, not been feasible to build a receiver which insureda constant band width, or channel, within relatively large wave lengthranges, with which therefore stations were received with constant bandwidth, but which in the presence of disturbances could be altered so asto possess greater selectance and a narrower width.

Now, the solution of this problem, according to the present invention,resides in that a constant band pass receiver arrangement of thecombined coupling type is provided with supplemental coupling means inthe different in particularity in the appended claims, the

invention itself, however, as to bothits organization and method ofoperation will best be understood by reference to the followingdescription taken in connection with the drawing in which I haveindicated diagrammatically several circuit organizations whereby myinvention inay be carried into efl'ect.

In the drawing,

Fig. 1 shows a pair of coupled tunable circuits of a conventionalreceiver and possessing .a'constant band pass characteristic,

Fig. 2 shows the circuit of'Fig. 1 embodying the invention,

Fig.3 shows a modified form of the invention.

Referring now to the drawing wherein like characters of reference in thedifferent figures represent like elements, Fig. 1 shows a circuit schemewhere L L are the inductance coilscompris'ed in a receiver operatingwith a constant band width. The mutual inductance between coils L and Lis designated by M.

The tuning condensers C and C are variable; coupling condenser G=1 1000cm; coils L and L have a diameter of 4 and a length of 6.5 cm, with 105turns, the distance of the coils. For A=250 m, then resulted in afrequency band of 18,500 cycles,

1 v n n n V 141 are inserted in each tuning circuit. These coils are sointer-coupled as at M that their coupling may be made so strong that thecoupling values resulting from the capacitive and inductive coupling ofthe two coils L L and condenser G can be reduced just to zero. Now, byany suitable mechanical means 3 the coupling between the two coi ls Zand Z can be reduced to zero; for instance,

as by turning the coil faces in relation to each other anyangle of 90degrees. 7

Between the circuits illlQlGQX-lSlJS then only the coupling due to theinductances L and L and the condenser C; in other words, the Y constantband width. If from this'position the-counter-active coupling Z Z begradually -ly introduced, then it will be possible to continuouslyadjust, or change, from constant band width to any desired band width ofthe receiver system so that, in the extreme case, the circuits act uponeach other like :two systems in very loose coupling relationship. j

Instead of turning the coils Z Z relation :to each other, the yariationof coupling may be accomplished by shifting a copper slab between thetwo coils Z and Z or using a short-circuiting ring. For example, in:Fig. 3, there is shown a receiver system comprising several pairs ofcoupled tuned circuits, wherein the change in the auxiliary couplingbetween the tuned circuits may be effected simultaneously. In thisfigure, the copper plates 0,, are mounted on a common shaft i and areshifted between the coils Z Z as well as Z 1' and operated from a commonknob The tubes 1, and 2 are conventional. The tuning condensers C C2, 0':C' may be operated by a common control 5.

dVhile I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is: V I 1. In combination, a pair of tunable cirgci' iitseach including a variable capacity and an invariable inductance, theinductances being coupled to provide magnetic coupling between thecircuits, an untuned condensive reactance common to both circuits, saidcoupled circuits possessing a constant band width characteristicthroughout a given frequency range, and additional means common to bothcircuits for controlling the band width characteristic.

2. In combination, apair of tunable circuits, each including a variablecapacity and an invariable inductance, the inductances being-coupled .toprovide magnetic coupling between thecircuits,ian untuned'condensivereactance common to both circuits, said coupled circuits possessing aconstant band width characteristic throughout a given frequency range,and additional means, including an auxiliary reactance in each circuit,common to both circuits for controlling the magnetic coupling betweenthe circuits.

3, In combination, a ,pair of tunable circuits, each including avaniablecapacity and an invariable inductance, the inductances :65 beingcoupled, an untuned reac tance common to both icirc-uits, said coupledcircuits possessing a constant band width characteristic throughout agiven frequency range, and additional means, including an auxiliarycoupling coil in each circuit and a variable shield disposed betweensaid auxiliary coils, for selectively varying the band passcharacteristic :to a sharply tuned characteristic.

ALEXANDER MEISSN-ER.

